Preform and production method therefor

ABSTRACT

For forming a preform of composite material, such as aluminum-based composite material (MMC) by using friction during the forming thereof, ceramic reinforcement, such as Al 2 O 3  and binder are prepared, and the prepared reinforcement and the silanor group binder are put into a die for press forming. During the forming, polycondensation occurs due to frictional heat generated between the fibrous or grain-like particles of the reinforcement and the silanor group binder to harden it, thereby obtaining a preform in which the particles of the reinforcement are fixedly connected to one another.

BACKGROUND OF THE INVENTION

1. 1. Field of the Invention

2. The present invention relates to a preform as a basis of a compositematerial, such as aluminum-based composite material (MMC), and aproduction method therefor.

3. 2. Description of Related Art

4. For the purpose of dispersing a reinforcement agent (herein afterreferred to as a reinforcement) throughout a composite materialuniformly and so on, in a conventional art, a preform of a predeterminedshape is produced, and it is impregnated with melted metal of amatrix-type metal by way of a forging method and an infiltration method,so as to produce a billet.

5. As a production method for the above-mentioned preform, a wet methodis commonly used as shown in FIG. 4. Namely, water, reinforcement(ceramic fiber) and binder are prepared, and after being mixed togetherand adjusted, the mixture is processed by press-forming. Next, afterbeing removed from the press, the press-formed product is dried so as toform the preform.

6. The wet method mentioned above, however, has problems in that thenumber of processes is large, and therefore the time for production islong. Further, the preform is easily broken (has high fragility), forinstance, when it is removed from the die, or during the drying andbaking processes. Furthermore, since water is required for the wetmethod, if a process for impregnating the preform with a melted metal islocated close to the process for producing the preform, there must beprovided means for avoiding contact between the melting metal and thewater, and therefore, the wet method comprises obstacles forindustrially performing the production processes from the preform to thebillet on an in-line process.

7. Moreover, with the wet method, metal powder, which is added forobtaining a composite material of high strength and high functionality,is oxidized. As a result, it is sometimes impossible to obtainsatisfactory results.

8. Further, according to Japanese Laid-open Patent No. Hei 5-255776(1993) and Japanese Laid-open Patent No. Hei 6-192765 (1994), etc.,there has been proposed a dry method.

9. In this dry method, ceramic reinforcement and inorganic binder mainlycontaining SiO₂ are mixed together, and after being formed by applyingpressure, the mixture is heated.

10. Further, a dry method using an organic binder has been disclosed inJapanese Laid-open Patent No. Hei 8-53724 (1996).

11. In this dry method, in particular in a case where the organic binderis used, the mixture must be heated to a high temperature (600° C. to1,100° C.) after being formed by the application of pressure thereto.Further, in the conventional dry method using organic binders, it isnecessary to add a large amount of binder into the reinforcement. Theseare all problems.

SUMMARY OF THE INVENTION

12. An object, in accordance with the present invention, for resolvingthe drawbacks in the conventional art mentioned above, is to provide apreform and a production method therefor, in which a preform can beobtained by the dry method without using water, which preform hassufficient strength and uses less binder.

13. Namely, in a preform, in accordance with the present invention,fibrous or grain-like particles in a ceramic reinforcement are bonded toone another into a polycondensation body produced by thepolycondensation of a binder of the silanor group, thereby achievingstrength higher than 200 kg/cm², being sufficient for the handlingthereof.

14. The ceramic reinforcement mentioned above can be any one containingfibrous, whisker-like, or grain-like shaped particles therein, and as anexample, aggregate alumina can be cited. The aggregate alumina comprisesalumina particles of 1-2 μm aggregating to secondary particles of sizesfrom several tens of μm to several hundreds of μm, and has a very largespecific surface. In accordance with the present invention, it ispossible to adhere the particles having a large specific surfacetogether (porous body).

15. Further, the preform can be improved in the characteristic valuesthereof, by adding thereto metal powder of Fe or Mg or the like.

16. Moreover, in accordance with the present invention, there isprovided a method for producing a preform, comprising the steps of:

17. mixing a binder of a silanor group with fibrous or grain-likeparticle-containing ceramic reinforcement in a ratio which is greaterthan 0.5 wt % and less than 2.0 wt %;

18. forming the mixture obtained in the above step and polycondensatingthe binder of silanor group through friction between the particles ofthe ceramic reinforcement and the binder of silanor group during theforming; and

19. bonding the particles of the ceramic reinforcement to one another ina polycondensation body produced by said polycondensation step.

20. As the silanor group binder, a mixture of silanor and siloxane, orpolymethylsilasesquioxane is appropriate. A chemical formula is shownbelow:

21. wherein R: —CH₃ or —H

22. In the case where the mixture of silanor and siloxane is used as thebinder, as is shown in FIG. 1, polymethyl siloxane having a molecularweight from 1,000 to 3,000 is produced by the polycondensation betweenthe silanor and the siloxane in a region of low temperature, and therebythe polymethyl siloxane bonds the particles of the reinforcement (Al₂O₃)to one another. Here, the region of low temperature indicates the regionof temperature at the time when the preform is formed, and is atemperature approximately in the range of 40° C. to 100° C.

23. However, if the formed preform is impregnated with melting metal,the polymethyl siloxane is heated to be changed into SiO₂.

24.FIG. 2 is a graph showing the relationship between the amount ofbinder added and the strength of the preform when thepolymethylsilasesquioxane is used as the silanor group binder. As isapparent from this graph, taking into consideration the handlingcharacteristics, such as setting the preform into a die after theforming thereof, it is necessary that the preform has a strength higherthan 200 kg/cm², and it is apparent that the polymethylsilasesquioxaneshould be greater than 0.5 wt % with respect to the reinforcement forobtaining such a strength.

25. On the other hand, since the strength of the preform is notadditionally improved even if the amount of polymethylsilasesquioxaneadded is increased above 2.0 wt %, it is therefore preferable that theaddition amount of the polymethylsilasesquioxane be greater than 0.5 wt% but less than 2.0 wt %.

26. There is also shown the strength when the polymethylsilasesquioxaneis changed into SiO₂ in FIG. 2. However, it is not necessary for thepreform in accordance with the present invention to be heated so thatthe polymethylsilasesquioxane is changed into SiO₂.

27. Further, though having made experiments on binders of the silanorgroup other than polymethylsilasesquioxane, the same result is obtainedin the relationship between the addition amount of the binder and thestrength of the preform obtained. Therefore, it is preferable that theamount of binder of silanor group to be added is greater than 0.5 wt %but less than 2.0 wt %.

28. Here, as the forming method of the preform, for example,press-forming or blow-forming is appropriate.

BRIEF DESCRIPTION OF DRAWINGS

29.FIG. 1 is a schematic diagram showing bonding reinforcement, in thecase where silanor and siloxane are used as the binder;

30.FIG. 2 is a graph showing a relationship between the addition amountof the binder and the strength of the preform, in the case wherepolymethylsilasesquioxane is used as the binder of silanor group;

31.FIG. 3 is a process diagram showing a production method of thepreform, in accordance with the present invention; and

32.FIG. 4 is a diagram showing a production method for the preform, inaccordance with the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

33. Hereinafter, detailed explanation of the embodiments according tothe present invention will be given by referring to attached drawings.

34.FIG. 3 is a process diagram showing the production method for thepreform in accordance with the present invention, and first of all, inthe present invention, ceramic reinforcement of Al₂O₃ or the like andbinder are prepared. At this time, for obtaining high strength and highfunctionality, it is possible to add metal powder, such as Fe, Mg or thelike.

35. Next, the prepared reinforcement and the binder (comprised, in thisexample, from a silanor group) are mixed and the mix is cast into a diefor press-forming. In place of this press forming, blow forming also canbe applied.

36. During the die forming, due to frictional heat generated between theparticles of the reinforcement and the silanor group binder, thepolycondensation causes the mix to harden, thereby fixedly bonding theparticles of the reinforcement to one another.

37. Hereinafter, concrete embodiments and a comparison will be given.

Embodiment 1

38. To 1,000 g of aggregate alumina (average particle diameter: 40 μm)is added 20 g of polymethylsilasesquioxane, and they are mixed by aV-type mixer for 30 min. so as to obtain a powder mixture that isuniformly dispersed. This powder mixture is poured into a press-formingdie, and is pressed with a pressure of 200 kgf/cm² to form a preformhaving, for example, a cylindrical shape, having a diameter of 150 mmand good handling characteristics.

39. This preform is set in a mold to be impregnated with melted metal ofaluminum alloy (5056) by a squeeze cast, thereby obtaining an Al₂O₃/Alcomposite material. Further, the volume containing ratio (Vf) of thepreform in the composite material being obtained is about 25%.

Embodiment 2

40. To 1,000 g of aggregate alumina (average particle diameter: 40 μm)is added 20 g of polymethylsilasesquioxane, and further 100 g of Fepowder is added thereto. After this, the mix is treated in the samemanner as in embodiment 1 to form the preform, thereby obtaining anAl₂O₃/Al composite material. Further, a volume containing ratio (Vf) ofthe preform in the composite material being obtained is about 25%.

Embodiment 3

41. To 1,000 g of aggregate alumina (average particle diameter: 40 μm)is added 20 g of polymethylsilasesquioxane, and further 100 g of Fepowder and 20 g of Mg powder are added thereto. After this, the mix istreated in the same manner as in embodiment 1 to form the preform,thereby obtaining an Al₂O₃/Al composite material. Further, a volumecontaining ratio (Vf) of the reform in the composite material beingobtained is about 25%.

Embodiment 4

42. Forming a preform under the conditions same to those of embodiment3, the preform and an aluminum alloy (5056) are set in a vacuum furnace.After being purged of nitrogen gas, it is heated to 850° C. under areduced pressure atmosphere of 200 hPa (hectopascal) to melt thealuminum alloy to be impregnated into the preform, thereby obtaining acomposite material. A volume containing ratio (Vf) of the preform in thecomposite material being obtained is about 25%.

Embodiment 5

43. To 1,000 g of aggregate alumina (average particle diameter: 40 μm)is added 20 g of polymethylsilasesquioxane, and 20 g of Mg powder isadded thereto. After this, the mix is treated in the same manner as inthe embodiment 4 to form the preform, thereby obtaining an Al₂O₃/Alcomposite material. Further, a voluminous containing ratio (Vf) of thereform in the composite material being obtained is about 25%.

44. Comparison

45. After adding 1,000 g of aggregate alumina (average particlediameter: 40 μm), 100 g of Fe powder and 20 g of Mg powder into water asolution containing silica sol and stirring them sufficiently, the mixis filtered and pressure-shaped by suction so as to obtain a preform ofa cylindrical shape having a diameter of 150 mm. It is further adjustedby a press-forming step so as to obtain a 25% volume containing ratio(Vf) therein, and this is put into an electric furnace to be heated to400° C., for the purpose of removing water therefrom and fixing thereof.After cooling, a preform having good handling characteristics can beobtained. With this preform, a composite material is obtained through anactivating compound method (a decompression permeation method) which isthe same as in embodiment 4.

46. Measured results of embodiments 1 through 5 and the comparison,i.e., the forming time of the preform, the strength of the compositematerial and so on, are shown in the Table below. From this table, inaccordance with the present invention, the time for forming the preformcan be reduced to ¼ that of the conventional comparison, through whichit is still possible to obtain sufficient strength. (See Table below.)TABLE Preform Metal Preform Forming Composite Reinforcement Vf PowderMethod Time Method Strength Embodiment 1 Alumina 25 — Dry Method 40 minSqueeze Cast 294 MPa Embodiment 2 Alumina 25 Fe Dry Method 40 minSqueeze Cast 372 MPa Embodiment 3 Alumina 25 Fe, Mg Dry Method 40 minSqueeze Cast 352 MPa Embodiment 4 Alumina 25 Fe, Mg Dry Method 40 minDecompression 352 MPa Permeation Embodiment 5 Alumina 25 Mg Dry Method40 min Decompression 300 MPa Permeation Comparison Alumina 25 Fe, Mg WetMethod 160 min  Decompression No melting metal Permeation permeates intothe preform

47. As is fully explained above, with the preform and the productionmethod therefor, according to the present invention, since the particlesof the reinforcement are bonded by polycondensating the silanor groupbinder, it is possible to obtain a strength higher than 200 kg/cm² whichis necessary for industrial handling of the preform.

48. In particular, in accordance with the present invention, since thepolycondensating of the silanor group binder is carried out usingmicroscopic friction between the ceramic reinforcement particles and thebinder when the preform is formed, no specific heating process norheating apparatus is required.

49. Further, in general, alumina powder has poor flowablity. Therefore,it cannot easily pass through a hole of a machine for measuringflowablity, having a diameter of 5 mm, for example. However, with theaddition of the silanor group binder to the reinforcement, it can easilypass through a hole of 5 mm diameter. This means that the melting metalof aluminum can easily permeate into the preform of the presentinvention.

What is claimed is:
 1. A preform of composite material which isimpregnated with melting metal, wherein fibrous or grain-like particlesof a particle-containing ceramic reinforcement are bonded to one anotherthrough a polycondensation body produced by polycondensation of asilanor group binder, thereby resulting in a strength higher than 200kg/cm2.
 2. A preform of composite material as defined in claim 1 ,wherein said ceramic reinforcement comprises aggregate alumina.
 3. Apreform of composite material as defined in claim 1 , wherein metalpowder of Fe or Mg is further added to said preform.
 4. A method forproducing a preform, comprising steps of: mixing a silanor group binderwith fibrous or grain-like ceramic reinforcement in a ratio which isgreater than 0.5 wt % and less than 2.0 wt %; forming the mixtureobtained in the above step and polycondensating the silanor group binderthrough friction between particles of the ceramic reinforcement and thesilanor group binder during the forming; and bonding the particles ofthe ceramic reinforcement to one another into a polycondensation bodyproduced by said polycondensation step.
 5. A method for producing apreform as defined in claim 4 , wherein said silanor group bindercomprises silanor and siloxane, and said polycondensation body comprisespolymethyl siloxane.
 6. A method for producing a preform as defined inclaim 4 , wherein said silanor group binder comprisespolymethylsilasesquioxane.
 7. A method for producing a preform asdefined in claim 4 , wherein said forming comprises press-forming orblow-forming.